All right, well, thank you, everybody, to our hot topics in exercise physiology as part of the Exercise Physiology Interest Group. It is our pleasure to invite Dr. George Brooks from Berkeley. He is a FIAD teacher from New York. He is an avid cyclist who has a yellow signed jersey from the Tour de France, and he knows how to get bikes on pennies on the dollar. He has connections from former champion cyclists, so that's a side job. You can ask him all about that, but today, he's talking about something much more important, which is the role of lactate, to really think lactate beyond its role as a typical waste product, and he'll be presenting his recent paper that was just published in Journal of Physiology of Lactate in Contemporary Biology, A Phoenix Has Risen, and if you have questions, go ahead and put it in either the chat or the Q&A, and I'll go ahead and moderate that, and George, thank you so much for coming. The floor is yours. Well, thank you very much. I'm very happy to be with you today and talk about this topic, which is really near and dear to my heart, and for this review paper, we just came on this idea of the phoenix because at the base here, you can see all the things that are traditional, burning, cramps, oxygen dead, anaerobic threshold, and the rest, but now we know that nature has designed biology to work for us, and lactate is a fuel, it's a signaling molecule, it's part of our microbiome, it's involved in the adaptive process, and so on. So time is short here, and we do want to have some conversation, so thank you for the introduction, and here's a brief outline. I want to talk about lactate shuttling and exercise and lactate oxidation and gluconeogenesis. Some of you know about this, these things already, and for some of you, this might be quite new. Number four here, the postprandial lactate shuttle is actually quite old, but we can fold old knowledge into our existing paradigm, and then we'll wrap up. So I want to start with a conclusion, and a wise professor once said to me, if you deal with professors, you really need to tell them the conclusion at the end, in the beginning, and in the middle. So there's glycolytic metabolism, there's oxidative metabolism, and the link between the two is lactate, because the product of one process can be the substrate for another, and this exchange between production and disposal, oxidative disposal, can occur within a cell, it can occur between cells in a tissue bed, it can occur between one organ and another, and I'll show some examples of that. So we know that lactate is a preferred fuel, actually over glucose in some instances, it's the major gluconeogenic precursor, and it's a signaling molecule. So 50 years ago, when I started in the field, everything to do with lactate was bad, it was a waste product, it was an indicator of oxygen inadequacy, it was a fatigue agent, really a metabolic poison. But now we know that times are changing, and we're still working on changing the basic biochemistry books and biology books, and actually there's a making some progress. So now we know that lactate has functionality, as indicated in this slide here in the green, and it's actually being used and tried in various clinical situations. So where do these ideas come from? Okay, so let me tell you about my history of interest. I was characterized as a cyclist, but I'm not a cyclist, but I was a runner. And here's a photograph, Madison Square Garden, 1962, 18 years old, freshman in college. And I said to my coach, why can't I make the Olympic team? And Coach Patty said, you have too much lactic acid, you have an oxygen debt. And I said, well, first I had original sin and I have lactic acid doses, what is this? Well, why do I have too much? And he said, go read about it. So I read about the work of this man, Nobel laureate, Otto Meyerhoff. And here's his classic experiment. He had a half of a frog, and that frog had no oxygen in it. So here's the frog hemicorpus, I think you can see my cursor. It's electrically stimulated to contract until exhaustion. There was no perfusion. And yes, there was fatigue. He won the Nobel Prize. So no hope, George. Too much lactic acid and oxygen debt. But others were active at the same time in founding really metabolic biology. And one was Otto Warburg, who received a Nobel Prize. He was actually Warburg's Meyerhoff's professor and received a Nobel Prize also for his work on cancer research. And if you just know a little German, there's a little bit of oxygen and a lot of oxygen. And these cancer cells always formed lactate, even in the presence of high oxygen. Then there were the Corys. And they received a Nobel Prize for their discovery, basically, of the recycling of lactate. So from the classic Cori cycle, glucose from the liver goes around the body to the muscle, becomes lactate, and just recirculates. So we have really contrary ideas. We have the oxygen debt. We have lactic acidosis. We have fatigue. And maybe we have cancer. But then we have the Cori cycle. And we have aerobic glycolysis. So in one sense, it seemed that lactic acid and lactate was all bad. But then there were some things that nature could do with it. So here's a traditional picture of how glycolysis works. Glucose, through the triose phosphates, gives us pyruvate. And if there's oxygen, then the pyruvate goes into the mitochondria. And then if there is no oxygen, then the pyruvate gets converted to lactate. We now know that this is not really true. Rather, glucose goes to pyruvate. And the lactate dehydrogenase step has the second greatest free energy change in glycolysis. So it's really inevitable that lactate's formed, regardless of the presence or absence of oxygen. We have measured lactate pyruvate ratios in tissues like muscle and the venous effluent of working muscle. And we can see that the lactate pyruvate ratio right now in us is at least 10. And with some moderate intensity exercise, the ratio will go to about 500. And also, this lactate then goes into the mitochondria. And then that's how it's disposed of. So in the early 1980s, we did quite a few experiments on laboratory rats. We could infuse tracer and take arterial samples. We studied them before and after training. We studied glucose. We studied leucine and alanine as far as amino acids. And we studied lactate. And we could study lactate and glucose simultaneously. So this is where the idea of a lactate shuttle came from. By measuring the lactate contents in arterial blood and in muscle, we deduced this. When a fast glycolytic fiber contracts, it forms lactate. And that lactate can go to an adjacent red fiber into the mitochondria and be oxidized. And then lactate can release from the white fiber muscle bed, could reperfuse the muscle red parts of the muscle within seconds during exercise. And again, the fate of lactate could be oxidation. And that's what we saw experimentally. So this idea was based on a muscle fiber type. But we didn't think about the brain. We didn't think about the liver. We didn't think about the heart. We didn't think about a signaling role. We knew there was exchange that's implied transport. But we didn't have any data on it. So then later in the 1980s, when stable isotopes came to the fore, we took our trusty subject. We did the first carbon-13 lactate infusion study. And here's a photograph of that. And here are some of the data which came from it. So there's always lactate production. And this is arresting people, men. And when they start to exercise, then, of course, the lactate production will go up. This is 50% of VO2 max. And this is 75% of VO2 max. So there's continuous lactate production at rest. And oxidative disposal is about 50%. And then at 50% of VO2 max, oxidative disposal jumps up and stays high even during exercise at 75% of VO2 max. So, oh, by the way, I put some photographs in here. So my associate, Dr. Thomas Budinger. And Masio was a graduate student. This was Masio's dissertation. And the reference is at the bottom. So just a couple of punchlines. So this lactate production occurs continuously. It's really the obligatory product of glycolysis. But it's disposed of continuously. So who knew? Who knew? Because the disposal is as fast as the production. You really don't see much change in concentration under many circumstances when we know the flux is really high. And then lactate production is high during exercise. But lactate is removed mostly by oxidation. So this is the way the system works. And who knew? Then the questions arose, OK, well, this is at the whole body level. But where in the body? Where is this lactate turnover taking place? Is it in the muscles, the heart? What's the role of the liver? And so on. So we took our trusty subject. And we took our bicycle ergometer and put it over a cardiac catheterization table. And a cardiac study lab. We could put in some venous lines, like one into the right biceps. It just would be sampling blood during exercise from an inactive muscle bed. And one would go into the coronary sinus, which is the venous drainage from the myocardium into the hepatic vein and one into the iliac vein. So these were fed up through a large vein in the arm into the right atrium and down the inferior vena cava and into the hepatic vein. And of course, we could take arterial samples at the same time. OK, so just not to race through things too fast, this is from Bill Stanley's dissertation. So we can see the substrate. This is from the arterial coronary sinus difference. Fatty acids are most of the fuel for the heart. That was pretty well established. There's always some obligatory glucose and lactate is a significant amount also. Then during exercise, we get a lactate as a blood lactate concentration rises. It becomes a major fuel for the heart. And fatty acids, even though the amount taken up quantitatively is the same or greater, percent wise it's less than this obligatory 4% glucose. So during exercise, blood lactate from working muscle fuels the heart. And this is a really good example of the lactate shuttle. But who knew that the muscles were feeding the heart? Well, not until we measured it. And then we wanted to address the issue of training because the lactate response to exercise and training is classic in work physiology and muscle physiology. So we decided to study and we studied men. We measured pulmonary gas exchange. We had femoral arterial venous catheterization on board so we can measure limb blood flow. And we had 313C lactate on board and diduderal glucose tracers. We took muscle biopsies. And we trained the men six days a week for two months. And they were supervised. Here's the study. This man is exercising and he has femoral, indwelling femoral arterial venous catheters. We're pulling blood samples simultaneously. We can know the lactate uptake and the CO2 production and labeled lactate uptake and labeled CO2 production, which basically 100%. This was in Gail Butterfield's lab at the Palo Alto VA. That's Dr. Gene Woffel and Dr. Ann Friedlander. So we published a number of papers on that, but here's one figure. This is lactate oxidation as a function. This is lactate oxidation in the leg. We can infer the muscle, but in the active leg, then times two, two legs. So how we can see a lactate uptake and oxidation increase sort of in this curvilinear fashion. And you can see the big difference after training. So we could show that during exercise, working muscle consumes and produces and consumes lactate and it disposes of it as oxygen, as CO2, because we could cut that from the 13 CO2 in the venous effluent. And so training improves not only lactate turnover capacity, but lactate oxidation capacity. And who knew? Previously, people thought that if you train, your lactate's lower because you produce less, but actually to the contrary, training allows you to generate more lactate, do more glycolysis, generate more lactate, but clear it. So then this brings us to one of my first loves in science. That's mitochondria and the mitochondria reticular network. This we published on this rat muscle and Hans Hoppler showed this, this is human skeletal muscle. And you can see the mitochondrial network here or reticulum. So that's the site of lactate disposal in the mitochondrial network. And then with Takeshi Hashimoto and others in our lab, we sought to find out, well, how do, how do mitochondria oxidize lactate? So here we have sort of the traditional paradigm, glycogen and glucose give us pyruvate. There is subsequently discovered a pyruvate transporter, but lactate is most of the carbohydrate flux. It permeates the outer mitochondrial membrane and there's what we call the mitochondrial lactate oxidation complex. And we can do this by co-precipitation, we can demonstrate this association by histology. And so, mitochondria can respire lactate and of course, for years we were doing pyruvate malate oxidation with mitochondria, but we just do lactate malate and we can see that mitochondria can respire lactate as fat faster than pyruvate and that's because of mitochondrial lactate dehydrogenase. And I really could do a whole separate seminar on that. So gluconeogenesis is another thing that happens in exercise and is one of the things that we benefit from exercise training. So recall, we infuse 313C lactate and so when that lactate becomes glucose, then glucose is heavy by mass plus one. So then we could see, and this is before exercise training, this is the rate of gluconeogenesis in these 12-hour fasted men. And then at rest, after training, we can see the increase in glucose production via gluconeogenesis. And then this is at 45% of VO2max before training, and this is 65%. So gluconeogenesis actually is less before training and hard exercise probably because shunting of blood away from the liver. But this here is the same absolute power output. You can see the training-induced increase in gluconeogenesis of exercise training. So this was 65% of max, now it's about 55% of VO2max. And this is the men again at 65% of max after training probably were getting some shunting away from the liver. So training improves the ability to maintain glycemia by improving capacity for gluconeogenesis from lactate. Well, who knew, actually not the Corys even, they never did human studies, they didn't study exercise or training. Okay, so one of the figures from the article we're talking about, we introduced the idea for the exercise community, but I think many people who are diabetologists know this already. There's the so-called indirect pathway of hepatic glycogen synthesis, sometimes also called the glucose paradox. And this phenomenon was featured by Dan Foster in the Banting Lecture way back in 1984. And to try to predict how this might work, we drew this figure for the Journal of Physiology. And I think where we will start to our attention is to look over here at the GI tract. So I'm going to crop this so we could see it better. So glucose enters the system. So if we look up here, the person has eaten some carbohydrate, and this carbohydrate will enter the gut, and the gut will release glucose, and it will go to the liver at first pass. Some of it is taken up and used to form glycogen in the liver, hepatic glycogen synthesis, but most glucose bypasses the liver, goes around the circulation, and goes to tissues such as muscle and the integument, where glucose is broken down to lactate. Then the lactate recirculates, goes around the body, comes back to the liver. This is why this is called the glucose paradox, because the liver is paradoxically making glycogen from lactate, or it's also alternatively called the indirect pathway of hepatic glycogen synthesis. But what this means is that dietary carbohydrate fluxes largely through the blood lactate pool before it's disposed of. And again, it can be disposed of by oxidation, about half of it is going to be removed by oxidation, and it's going to be the major glycogenic precursor. This is in our Phoenix paper, but it's actually not new, but it fits in with the whole paradigm of carbon flux through the body in the form of lactate. Now what's probably the newest part of the field is the role of lactate as a signal. There was an orphan receptor, GPR 81, which was discovered by Ahmed and others to be a lactate receptor. In terms of, this is an adipocyte, and this is from his paper. So we have a insulin receptor and glucose uptake, and glucose uptake is going to be stimulated by insulin, and glucose will undergo glycolysis and give us lactate, and then the lactate will be released and go to this lactate receptor called HCAR1, hydroxycarboxylic acid receptor. And there are a family of these, HCAR1 is the lactate receptor. And that works through cyclic AMP and CREB, and it functions to inhibit the polysis. And so this is diagrammed here to be an autogen signal, but lactate from exogenous lactate from another cell or from another organ in the body can reach white adipose. And we know from experience and by actually measuring fatty acid appearance and the polysis during exercise that when we exercise hard, our fatty acid levels fall and fat ceases to be a fuel, and one of the reasons is that the polysis is inhibited by lactate. So then by being trained, you can clear the lactate, and then therefore that allows for more lipid oxidation. And also from a paper that's now online and in press, we point out that when we form lactate from pyruvate, there's a big redox change. And then when there's some cells that are driver cells, this is glycogen and this is glucose, and when we have glycogenolysis and glycolysis, we're going to make lactate, then they're going to be recipient cells where there's a rich mitochondrial reticulum or there's gluconeogenesis in the liver and kidneys. So that when we produce lactate, the lactate is more reduced when it's consumed, and that oxidation process in the disposal site changes the NAD and ADH ratio, which are powerful signals in metabolic regulation. So to summarize this paper, there's glycolytic metabolism, there's oxidative metabolism, the link between the two is lactate, there's utility in this, lactate is a preferred fuel. So if we look at glucose versus lactate flux rates in different conditions, we can see lactate is preferred. It's the major gluconeogenic precursor, and now we know it's a signaling molecule. So I think what's new about this paper really are two things. It's recognizing that there's a postprandial lactate shuttle, sometimes called the indirect pathway of hepatic glycogen synthesis, and that lactate is a signaling molecule. And if you don't believe me, you can read about this in the literature. So our host today, Dr. Qiao, and all-star cast of people, including Dr. Lanza, published in Nature Review on extra kinds and their role in health and disease. And we have a paper coming out in the Journal of Applied Physiology, which talks about myokines and extra kinds, but particularly the role of lactate as a signal, which I tried to go over today and introduce the concept. So just to summarize, again, there's utility in the formation of lactate, and it provides an essential means for carbon distribution in normal physiology and also in pathology. Thank you very much. Thank you so much, George. Appreciate it. And we already have a question from Ian. As you can see here, of course, we loved your talk. Is the monocarboxylic transporter trainable? For example, how much can the increase in lactate oxidation and uptake with exercise training be explained on the basis of better transport, or is it primarily due to upregulated machinery to use it, such as mitochondrial biogenesis? Yeah, so that's a good question. So I don't know about trainability of HCAR1, but we do know about the trainability of MCTs, lactate transporters. And they go up in our study. In this study we did on men, they increased to 80%. So we can have a significant increase in the transportability of lactate. But we also know that in the study we basically also increased, we doubled the mitochondrial mass. Excuse me. So we need transporters, excuse me folks, we need transporters, but we need disposal sites. And in the main, it's the mitochondrial reticulum. So by increasing the mitochondrial mass with training, that really facilitates the exchange process, because this is how we establish the disposal, that is by making gradients. Any other questions from the audience? All right, we got another one. Hi, it's Tana Ekelband. This talk is great. After we eat, lactate concentrations go up. As a signaling molecule, does lactate play a role in the brain to alter energy intake? Okay, I did mention the name of Takeshi Hashimoto. He did a marvelous job in defining the mitochondrial lactate oxidation complex. And Takeshi went to Japan. He did a research fellowship with Neil Secker. And Neil's famous name in muscle and exercise physiology was he's an anesthesiologist. And so in Copenhagen, they were able to measure brain uptake of lactate and found that when you exercise, the brain increases its glucose consumption. Not very much, but it switches over to lactate, which becomes available. The blood-brain barrier is basically a series of transporters, including MCTs. And so when you raise the blood level of lactate by exercising, Hashimoto and Secker and colleagues could show that increased arterial lactate concentration in exercise allowed the brain to take up more lactate. And also, part of the team was a psychologist. And this is not my field, but there are various basic tests of intellectual capacity, executive function that people can take. And there are screen-driven tests. And so they found that during exercise, when their lactate consumption was high, not only was there an increase in secretion of brain-derived neurotrophic factor, but the people got smarter. They did better on the tests. And subsequently, others have just skipped the exercise and just infused lactate and seen increases in BDNF secretion in the brain, brain-derived neurotrophic factor. So thank you for the question. So I think Dr. Chow mentioned that I was, earlier in my career, a phys ed instructor. But this is really one of the great ideas that maybe doesn't permeate the physical education professional discipline. The kids get smarter by having been exercised. And also, they'll be more attentive, and they'll be better students, and they're really cued in to do better in school. So, George, we have another question in the Q&A from Mark Christensen. He says, if he recalls correctly, using 2,13-glycerol, Hellerstein shows that gluconeogenesis accounts for about 33% of fasting hepatic glucose production. Using 3,13-lactate, it appears that you're noting a much lower percentage of hepatic glucose production from gluconeogenesis. Did he read your slide correctly? So maybe to go back to that slide? Yes, I'm happy to do that. People can deal with this jumping around. Hey, Mark, I know Mark's sort of a neighbor here in the Bay Area. We did a study with glycerol. We did label glycerol, and we found in our human subjects that glycerol is really a poor gluconeogenic precursor. So this is the percentage of gluconeogenesis that comes from lactate. So Dr. Christensen is correctly saying lactate is not the only gluconeogenic precursor, but in our experience, it's the major one. We've tried glycerol, and in our hands, glycerol didn't perform as well as lactate. But in an exercise, what's going to happen is the glycerol concentration is going to fall. And so the lactate concentration is going to rise. It's probably another discussion we could have on another day about which is a major gluconeogenic precursor in various conditions. All right, any questions from anybody else? I see one from Todd. Maybe. That is class, listen to the seminar. So maybe I have a question while other people have gathered their thoughts and we're almost done. There's a very interesting paper in nature that just got published. I put in the PMID there. And it was the idea of using lactate and it combines with phenylalanine to make a new metabolite that suppresses appetite. Are you aware of that, George? Yeah. What are your thoughts on that? And maybe sort of the lactate plus in terms of signaling of that. Yeah, so it's a combination of lactylation of phenylalanine. But I looked at their paper and actually in our review which is online, there's about 200 times more lactate than lactate phenylalanine. So maybe, so lactate is upstream. So if it's lactate phenylalanine which is affecting the hypothalamus, that's good. The upstream signal is lactate. And here we're working on, we have an aging study going. And so we're looking at this idea of lactylation of histones first that was seen. And now we can see lactylation of many amino acids. So I said, no, so thank you for the question because lactylation of a variety of things is happening. So it's a whole new field. And I think one of the things that gives us satisfaction about this effort for the first 20 years nobody believed us at all. And now people are doing experiments and they're taking the field and expanding the field. So lactylation of histones, lactylation of amino acids and their various roles in biology. So we know that again, if you exercise hard you're not gonna be hungry. And so there's some mechanism for that. We know that lactate will inhibit lipolysis and I didn't mention it, lactate also inhibits CPT2. So activated fatty acids can't get into the mitochondria. So at both ends of the process is going from lipolysis to fatty acid oxidation at the mitochondrial level. Lactate is interfering with both ends. So again, that's an advantage of training. You clear the lactate and that allows you really rapidly to switch into a fatty acid metabolism. We saw that some years ago when Greg Henderson in our lab, we studied lipolysis during exercise and recovery. And you can see when lactate's high, lipolysis is low. And then from the gas exchange R and from the oxidation of 13 C level palmitate it's really low until the lactate's cleared. So George, we have one final question and then we'll wrap it up. This comes from Todd. It said, in your studies, have you noticed any sex differences in lactate oxidation in a low to moderate intensity exercise given that women tend to metabolize more fat than men? Yeah, so Todd knows our work really well. And I guess he's one of the first people to talk to me about that. So Todd knows our work really well. And I guess he's prompting me to say that women are better fat burners than men. So now in terms of these lactate studies we haven't done them on women. We haven't had the support and with the putting these catheters in England area and human subjects. I just don't wanna talk to some father whose daughter got a hematoma because of our studies. So we haven't done it. And Todd knows very well, we've worked together at high altitude and Pike's Peak. So women are better fat burners. That's true. Women will typically have lower lactate levels than men for a given relative exercise intensity. And maybe that's one reason women are better fat burners than men. But the issue is unaddressed, I think. All right, we'll go ahead and wrap this up. Thank you again, George, for coming. And of course you will be our featured speaker at our professional interest group discussion at the ADA on Saturday, June 24th, from 1130 to 1230. So people who are going to ADA, you'll hear George again and there'll be a nice debate. And thank you again so much. And congratulations on the paper. Thank you very much. Okay. Thank you again. Bye everybody. Oh, we got some applause coming through.

lactate

exercise physiology

fuel

signaling molecule

lactate shuttling

gluconeogenic precursor

lactylation